#include <iostream>
using namespace std;

struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
};
class Solution {
    TreeNode *mergeTrees(TreeNode *t1, TreeNode *t2) {
        if(t1 == nullptr) return t2;
        if(t2 == nullptr) return t1;
        t1->val += t2->val;
        t1->left = mergeTrees(t1->left, t2->left);
        t1->right = mergeTrees(t1->right, t2->right);
        return t1;
    }
};